This invention relates to an electronic component and, in particular, to an electronic component 2 of a surface-mounted type or a leaded type such as an inductor (L), a capacitor (C), an electric resistance element (R), a thin film EMI filter, a common mode choke coil, a current sensor, a signal transformer, and a composite electronic component comprising an integral combination of the above-mentioned electronic components.
A conventional multilayer interconnection board is disclosed in Japanese Unexamined Patent Publication (JP-A) No. 4-167596 (167596/1992) (Reference 1). As shown in FIG. 1, the multilayer interconnection board comprises a ceramics substrate 51 mainly containing silicon, alumina, and the like, and a conductive interconnection layer 52 comprising Cu formed on a predetermined region of the ceramics substrate 51. Then, an entire surface of the ceramics substrate 51 and the conductive interconnection layer 52 is coated with an insulator resin layer 53 of benzocyclobutene (BCB). After a photo resist pattern is formed on the insulator resin layer 53, the insulator resin layer 53 of BCB is etched to form via holes 54. After the via holes 54 are formed, a Cu film is overlaid an entire surface by sputtering and then etched. Alternatively, after a Cr or Ti film is overlaid the entire surface by sputtering, a Cu sputtered film or a Cu or Au or Al plated film is formed to thereby provide a conductive interconnection layer 55.
On the other hand, Japanese Unexamined Patent Publication (JP-A) No. 3-201417 (201417/1991) (Reference 2) discloses an electronic component of the type illustrated in FIG. 2. The electronic component comprises an insulator substrate 101 of, for example, alumina. On the insulator substrate 101, an insulator resin layer 102 of polyimide resin and internal conductor patterns 103 and 104 of Ti, Ti-Ag, or Ag formed by sputtering are alternately stacked. Then, an end portion of the insulator resin layer 102 is removed to expose an end portion of the uppermost conductor pattern 104. Thus, a high frequency coil 100 is formed as the electronic component.
Practically, a terminal underlayer portion is formed on the side surface of the electronic component so as to connect with the end portion of the conductor pattern 104. The terminal underlayer portion is covered with a conductor layer which extends from an end of the upper surface through the side surface to an end of the lower surface of the component. Thus, an external electrode terminal portion is formed.
Reference 1 describes the multilayer interconnection board which is neither an electronic component as a circuit element nor an electronic component having a plurality of circuit elements.
On the other hand, when the electronic component of the type disclosed in Reference 2 is manufactured, the insulator layers and the conductor layers for a plurality of the electronic components are alternately stacked on different portions of the insulator substrate of a relatively large size. Thus, a plurality of the electronic components are formed on the single insulator substrate. Thereafter, the insulator substrate is cut to separate the individual electronic components. However, since the insulator substrate comprises a very hard material such as alumina, cutting cost is high in the cutting process. In addition, occurrence of chipping of the insulator substrate results in high fraction defective and low yielding percentage.
In the above-mentioned structure, the irregularity of the underlying conductor pattern layer reflects or is reproduced on the surface of the insulator resin layer formed thereon. This results in the unevenness of the overlying conductor pattern layer stacked on the insulator resin layer. In this event, a desired characteristic can not be achieved.
Furthermore, the moisture contained in the ambient air enters into the electronic component through a gap between the insulator resin layer and the electrode terminal portion. This brings about corrosion of the conductor pattern and fluctuation of the characteristic. As a result, the quality of the electronic component is considerably deteriorated.
It is therefore an object of the present invention to provide a highly reliable electronic component which can be easily manufactured and reduced in size and which has characteristics desired.
It is another object of the present invention to provide a circuit element comprising at least one of a low pass filter, a common choke coil, a transformer, an inductance, a capacitance, and an electric resistance each of which is formed as the above-mentioned electronic component.
According to this invention, there is provided an electronic component comprising an insulator substrate, a layered member composed of a plurality of insulator resin layers and a plurality of conductor pattern layers alternately stacked on the insulator substrate to form a first conductor line and a second conductor line each of which comprises at least one conductor layer, first and second external electrode terminal portions connected to opposite ends of the first conductor line and covering first and second areas of side surfaces of the layered member and the insulator substrate, respectively, and a third external electrode terminal portion connected to one end of the second conductor line and covering a third area of the side surfaces of the layered member and the insulator substrate. The first and the second conductor lines have magnetic and electrocapacitive coupling with each other.
According to this invention, there is also provided a common mode choke coil comprising the above mentioned electronic components. The common mode choke coil further comprises a fourth external electrode terminal connected to the other end of the second conductor line and formed on the side surfaces of the layered member and the insulator substrate at a fourth area different from the first through the third external electrode terminal portions. Each of the first and the second conductor lines have a pattern circulated on different conductor layers, the number of turns in both lines being equal to each other. A pair of the first and the third external electrode terminals and another pair of the second and the fourth external electrode terminals serves as an input terminal pair and an output terminal pair, respectively.
According to this invention, there is also provided a transformer comprising the above mentioned electronic component. The transformer further comprises a fourth external electrode terminal connected to the other end of the second conductor line and formed on the side surfaces of the layered member and the insulator substrate at a fourth area different from the first through the third external electrode terminal portions. Each of the first and the second conductor lines have a pattern circulated on different conductor layers. A pair of the first and the second external electrode terminal and another pair of the third and the fourth external connection terminals serves as an input terminal pair and an output terminal pair, respectively.